Reaction products of aromatic compounds, such as alkylated aromatic compounds, are common petrochemical products that are useful as intermediates for the preparation of other widely-used industrial compounds. For example, cumene (also known in the art as isopropyl benzene) is widely used as an intermediate in the production of phenol and acetone, and ethylbenzene is widely used as an intermediate in the production of styrene.
Alkylated aromatic compounds are generally prepared by reacting aromatic compounds with olefins in the presence of an aromatic alkylation catalyst, such as phosphoric acid catalysts or recently developed zeolitic acid catalysts. Processes of and systems for producing alkylated aromatic compounds are known in the art.
Aromatic feed including aromatic compounds to be reacted often includes nitrogen-containing impurities such as indoles; pyridines; quinolones; diethanol amine (DEA); and morpholines including N-formyl-morpholine (NFM) and N-methyl-pyrrolidone (NMP). The presence of nitrogen-containing impurities in aromatic feed is generally undesirable for various reasons. For example, nitrogen-containing impurities may form deposits on aromatic alkylation catalysts during alkylation of the aromatic compounds, thereby contaminating the aromatic alkylation catalysts. Such contamination adversely affects catalyst performance and catalyst life and increases regeneration frequency of the aromatic alkylation catalysts. During regeneration, accumulated nitrogen compounds and coke are combusted from the aromatic alkylation catalysts to regenerate the catalysts. Even very low nitrogen concentrations in the aromatic feed may increase catalyst regeneration frequency due to formation of deposits from the nitrogen-containing impurities on the aromatic alkylation catalysts.
Techniques have been sought to address the impact of nitrogen-containing impurities from aromatic feed on the aromatic alkylation catalysts. For example, techniques have been developed for treating the aromatic alkylation catalysts themselves, such as through desorption of the impurities from the aromatic alkylation catalysts after contamination thereof. As another example, adsorption techniques have been developed, using guard bed systems, for adsorbing nitrogen-containing impurities from aromatic feed prior to alkylation in the presence of the aromatic alkylation catalyst. In the guard bed systems, the aromatic feed is passed over a fixed bed of adsorbent material that is capable of chemically adsorbing the nitrogen-containing impurities from the aromatic feed. However, existing guard bed systems are generally incapable of adsorbing all nitrogen-containing impurities from the aromatic feed. As a result, residual nitrogen-containing impurities generally remain in the treated aromatic feed after passing through the guard bed systems. Simply increasing capacity of the guard bed systems is an undesirable and often imperfect approach to removing greater amounts of nitrogen-containing impurities from the aromatic feed due to the nitrogen-containing impurities in the aromatic feed having different degrees of basicity with some of the nitrogen-containing impurities having basicity that falls outside of an operating range of the guard bed systems.
Accordingly, it is desirable to provide processes and systems that are configured to assist with removal of residual nitrogen-containing impurities from aromatic feed after adsorption of a portion of the nitrogen-containing impurities from the aromatic feed. In addition, it is desirable to remove the residual nitrogen-containing impurities from the aromatic feed without increasing capacity of the guard bed systems. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.